I remember it as a rat-infested dump. Water dripped down walls. Wires hung from ceilings. Pigeons colonised turrets and rafters. Gormenghast could not do justice to the profile of that destitute old lady, slumped at the far end of Euston Road. Poor St Pancras hotel embodied the contempt of modernism for anything old, stylish, romantic and, above all, Victorian. The place should be left to rot, an example to any who might find beauty in antiquity or economy in restoration.

Thirty years ago I staged a "flash" party in the derelict staircase of St Pancras, to draw attention to its plight. British Rail and its architects had fought for years to demolish it in favour of a new King's Cross in the style of Euston. So we crammed the flights of steps with rail enthusiasts, put trumpeters on the landings and toasted the old lady with champagne. Valiant campaigners from the Victorian Society led by John Betjeman and others had managed to get the building listed, but at the time it seemed at risk of collapse. Nobody cared.

Illustration by Satoshi Kambayashi

Last month St Pancras hotel finally reopened to defy the forces of darkness. It is restored to its old magnificence, courtesy of three noble firms, London and Continental, Manhattan Lofts and Marriott hotels. The finest booking hall in Europe clinks with cocktails. The murals on the old staircase throb with colour. Arches leap across corridors and gilt drips from vaulting. Victorian restaurants, bedrooms and bars are booked solid. Sometimes, just sometimes, beauty wins.

By happy coincidence, next week also marks the bicentenary of the birth of the creator of St Pancras, Sir George Gilbert Scott. He was the most prolific architect of his age, and possibly of all time, and also the most unsung. His works spanned the empire, from New Zealand to Newfoundland. In England alone, he designed 800 buildings and oversaw hundreds more restorations. He produced churches, schools, hospitals, workhouses, asylums and vicarages galore. He has 607 structures listed as historic, more than any other architect (next is Lutyens, with 402), including the Albert Memorial, the Foreign Office, Edinburgh Cathedral and the universities of Glasgow and Bombay. Scott restored 18 of the 26 English medieval cathedrals. From his office his grandson, Giles, designed Liverpool Cathedral, Battersea power station, red phone boxes and what is now Tate Modern. Scott towered over his profession, yet he has no biography.

At least the Victorian Society has done him the honour of a celebratory magazine, adorned with a picture of Scott's great colonnade at Bombay university in rich Venetian gothic. The issue is more than a hymn of praise. It seeks to explain the role of taste in governing the changing appreciation of historic style. For decades, as Ian Dungavell points out, Scott was seen as a vandal, "the bête noire of the society for the protection of ancient buildings", for what was seen as his over-restoration of medieval churches. This helped fuel hostility to Victorian architecture through most of the 20th century. When Scott died, his enemy William Morris hailed "the happily dead dog".

The Victorian Society has recovered Scott's reputation not as a destroyer of old buildings but as their scholarly rescuer. He was a meticulous lover of medieval architecture, reinstating hundreds of medieval churches in the manner in which he envisaged their builders had intended. He confronted an Anglican inheritance that had been neglected and was on the verge of collapse. He had to rebuild Chichester cathedral tower after it actually fell down, and used hydraulic rams to prop up St Albans Abbey.

As Gavin Stamp points out, "Scott treated buildings with careful, loving respect and intuitive structural knowledge", so as to put them back to the use for which they were designed. At one derelict site after another, he had his assistants comb the ground to find fragments of medieval stone to re-erect and copy. He was a devoted follower of Pugin, giving him pride of place in the parade of architects on the Albert Memorial, with his own profile carved, diminutive, behind him. Morris's attack was unfair. Scott merely rejected Morris's authenticity of material in favour of authenticity of style. Had it not been for him, hundreds of English churches would today be ruins, stabilised in the picturesque wreckage beloved of the old ministry of works, with fragmented walls and gaunt gables set in immaculate government lawns.

Scott was certainly a partial gothicist. His argument with Palmerston in 1858 over the design for a new Foreign Office in Whitehall saw an epic "battle of the styles". Palmerston pitted his imperial classicism against Scott's city-state medievalism. The plans passed through a compromise byzantine before coming to rest on the present Italian renaissance. Rarely was meaning in architecture subjected to such furious public debate, battle being joined in the press and in parliament, those being the days. A Tory minister, Geoffrey Rippon, tried to demolish the building as "obsolete" in 1963 but was stopped.

I love St Pancras but see Scott's Albert Memorial as a more exquisite masterpiece. Restored by English Heritage in 1998, it is England's Taj Mahal, encasing the golden statue of Victoria's departed Albert in a soaring shrine in honour of western civilisation. Promenaders arriving at the Albert Hall next week should turn awhile from that pompous bosom of a building and admire this supreme work of gothic art. Catch it above all as an imperial sun sets across Kensington Gardens.

What the neglect of Scott illustrates is how fickle is the eye of fashion. The dirt that came to encase his buildings, much of whose appeal lay in ornament and colour, was mistaken for ugliness. His attempt to rescue old buildings was seen as philistine, and judged worthless. Anything to do with the medieval revival was regarded as pastiche. The contrasting blank facades and unadorned interiors of 20th-century modernism were seen as clean, socialist and virtuous.

All architecture is a pastiche of something, none more so than today's "neo-modernist" revival. Scott was wholly up to date in his use of such materials as steel, concrete, plate glass and the technology of steam. He even put a modern bathroom on each floor at St Pancras. But he understood the spiritual exhilaration of the vertical line, the pointed arch and the soaring turret. In an age of relentless novelty, he understood that architecture could reassure people, that buildings could perform new uses yet offer comfort in continuity.

What was sad in the campaign to save St Pancras was the absence from it of Scott's own profession of architect, to which anything old is a nuisance and anything new is a fee. Anyone wishing to see what today's architects preferred need only trot down the road to Euston station, a building with no respect for any style past or present, indeed with no sense of visual delight at all. I gather it is to be demolished. I have struggled to see Euston as the St Pancras of our age but failed. If there is a "save Euston" society being formed, I am afraid it is not for me.

• This article was amended on 12 July 2011. The original said Sir Giles Gilbert Scott was the son of Sir George Gilbert Scott. This has been corrected.